Molecular Dynamics Phenomena of Water in the Metalorganic Framework MIL-100(Al), as Revealed by Pulsed Field Gradient NMR and Atomistic Simulation

Abstract

Measured, via pulsed field gradient (PFG) NMR, and computed molecular dynamics (MD) were utilized for the study of the phase equilibrium and kinetics of water sorbed in a bed of MIL-100(Al) crystallites. The computations rely on our recent methodology for modeling water equilibria and dynamics in the Fe-homologue MIL-100 crystal; in that sense, the particular NMR technique serves also as a validation tool of the previous simulation work which is adapted to the current system. In addition, a computational scheme for assigning partial charges on the host framework atoms was devised; it involves density functional theory (DFT) combined with electronegativity equalization method (EEM) calculations. The derived this way electronegativity, hardness, and gamma parameters for the specific MIL-100(Al) atoms can be used in EEM calculations of other aluminum metalorganic frameworks (MOF) bearing similar atom types. The thermodynamics predictions obtained via MD, comprising equilibria, enthalpies, adsorbate probability densities, and host's terminal species effects, were compared with data from the real system's phase equilibria measured in this work. The intracrystalline self-diffusivity of the sorbed water was extracted by means of the spin echo curves obtained by PFG NMR for various guest loadings as a function of observation time and a theoretical short-time expansion of the diffusion coefficient of random walkers, assuming spherical particles under reflecting boundary conditions following Mitra et al. The experimental activation energies for diffusion confirmed previous, in MIL-100(Fe), and current modeling results, with respect to the adsorbed water dynamics and singlet probability density distribution.

Insights into the water adsorption mechanism in the chemically stable zirconium-based MOF DUT-67 – a prospective material for adsorption-driven heat transformations

“…21 Currently, several waterstable MOF materials are considered the most promising for this type of application. Henninger and co-workers extensively studied the water adsorption behaviour of CAU-10-H 22 (CAU stands for Christian-Albrechts-Universität zu Kiel), aluminium fumarate 6 and MIL-100(Al) 23 (MIL stands for Materials of Institute Lavoisier) for heat exchanger applications. Furthermore, authors developed a full-scale heat exchanger, coated with an aluminium fumarate framework.…”

Molecular Mobility of Tert‐butyl Alcohol Confined in a Breathing MIL‐53 (Al) Metal‐Organic Framework

“…Despite a notable number of the catalytic processes successfully tested for MOFs, the dynamics properties of the reactants involved remain unknown for the most of the cases. In fact, with a very few exceptions, the experimental observation of the molecular mobility in MOFs was limited, so far, to relatively simple hydrocarbons and small molecules such H 2 , CO 2 or water . In addition, certain MOFs are capable of “breathing” by reversible change of the pore size upon guest molecules adsorption .…”

“…In fact, with a very few exceptions, [8] the experimental observation of the molecular mobility in MOFs was limited, so far, to relatively simple hydrocarbons [9] and small molecules such H 2 , [10] CO 2 [11] or water. [12] In addition, certain MOFs are capable of "breathing" by reversible change of the pore size upon guest molecules adsorption. [13] Despite the breathing phenomenon itself has received much attention, its effect on the molecular transport has remained poorly understood with a few exceptions, [14] again related to the hydrocarbons.…”

2H Solid‐State NMR Spectroscopy Reveals the Dynamics of a Pyridine Probe Interacting with Coordinatively Unsaturated Metal Sites of MIL‐100(Al) Metal–Organic Frameworks

“…In this regard, the information on the dynamics of the molecular probe in such a state can yield valuable information about the effect of network linkers on the potential accessibility of the reactants to catalytically active sites . To our knowledge, such work was performed only for the NO and water . Yet the typical acidity probes such as pyridine were not considered for their dynamical behavior in MIL‐100 so far.…”

“…[14] To our knowledge,s uch work was performed only for the NO [16] and water. [17] Yett he typical acidityp robes such as pyridine were not considered for their dynamical behavior in MIL-100 so far.…”